The invention is in the field of mounting techniques for a semiconductor component, in particular a memory element. The semiconductor component has a housing or housing body which is formed around the semiconductor component after the semiconductor component is brought into contact with a lead frame.
Published, Non-Prosecuted German Patent Application DE 196 25 384 A1 discloses a method of producing a component and a lead frame. In order to provide an electrical contact and possibly also to distribute and dissipate the energy converted into heat in an electronic component, a lead frame is used. Such a lead frame is normally produced with a large number of further lead frames in a coherent strip and, in particular, includes a carrier region (island) for the component and input or output lines for providing an electrical contact, which in the following text are also referred to as conductor leads or conductor tracks. The lead frame can in principle also be configured to implement the so-called lead on chip (LOC) technique, which is known per se. The lead frames are initially coherent in the strip. The individual lead frames and thus the individual components are only separated at an advanced mounting stage.
During the mounting of components, the conductor leads are normally connected to one another by connecting webs formed between them in the form of a so-called xe2x80x9cdam barxe2x80x9d. In addition to increasing the mechanical stiffness during the fabrication process, the dam bar is used with its upper or lower side as a defined sealing surface for the injection molds. At the dam bar, the molding tools seal off a housing volume which is to be filled with a press-molding compound and in which the housing body is produced. The housing body encloses the component and the central regions of the lead frame after the injection of the press-molding compound. Subsequent to the formation of the housing body, the dam bar, that is to say the webs or intermediate sections connecting the individual conductor leads to one another, are removed, so that the conductor leads are electrically isolated from one another. In addition, the conductor leads are bent into predefined shapes in order allow a contacting for an operation of the component after undergoing functional tests. The contacting may be achieved by soldering.
For the purpose of the aforementioned functional tests, the components have to be introduced into test sockets, respectively specific to the component, and electrical contact has to be made with them. Given the increasingly smaller dimensions of the conductor leads and the conductor-track spacings, very precise alignment and centering of the component in the respective test socket is required. However, the close tolerances to be complied with cannot always be ensured in the case of conventional components, because of considerable variations in the external dimensions of the housing bodies. The alignment and centering of the components is normally carried out via stops on the test socket which cooperate with housing-body edgesxe2x80x94in particular the corners of the housing body. The position of the housing-body edges or corners varies considerably in relation to the conductor leads with which contact is to be made. The reasons for this are, in particular, the comparatively high fabrication tolerances with regard to the external dimensions of the housing bodies, and the press-molding compound flash or burr-type parting line produced during the formation of the housing body.
In the case in which the components are fixed in the test sockets by hold-downs acting on the leads, in the worst case a bending of the leads and therefore damage to the component can occur, as a result of which the component may be damaged and even become unusable.
It is accordingly an object of the invention to provide a method for positioning a component mounted on a lead frame in a test socket which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type and which allows the use of the structural configuration of the component as a reference when positioning the component, and which allows a reliable, highly accurate and reproducible positioning of the leads.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of positioning a component mounted on a lead frame in a test socket, which includes the steps of:
providing a lead frame with outwardly directed conductor leads subdivided into outer leads and inner leads, the conductor leads being connected to one another by connecting webs (dam bars) formed between the conductor leads, at least one of the connecting webs having an intermediate section provided between two of the conductor leads and the lead frame having an extension on a side of the intermediate section facing the inner leads;
mounting a component on the lead frame and electrically contacting the component and the inner leads;
enclosing the component in a press-molding compound for forming a housing body and forming a contact face between the extension and the press-molding compound;
removing the intermediate section and thus transforming the contact face into a separating face formed on the housing body; and
using the separating face as a reference for positioning the component in a test socket.
In other words, according to the invention, the structural nature of an electronic component is used as a reference when positioning a component, which includes at least one electronic element, a housing body and a lead frame. The component is mounted on the lead frame and, for the purpose of external electrical connection, is brought into contact with outwardly leading conductor leads on the lead frame. The component and the central region of the lead frame are enclosed in a press-molding compound which forms the housing body. The lead frame initially has an extension, which can be separated from the lead frame after the formation of the housing body and the extension can be removed from the housing body, so that a separating face which is accessible from the outside is produced between the extension and the housing body. The separating face is used as a reference when positioning the component.
A significant advantage of the method according to the invention is that, at the points on the housing body which are critical for the alignment and centering, no press-molding compound flash or burr can remain and/or be broken out of the press-molding compound in an undefined way. Thus a highly accurate reference face or reference edge is produced on the housing body. The reference face or reference edge is advantageously simply produced in that during the removal of the extension on the housing body, the separating face originally formed between the extension and the press-molding compound of the housing body is exposed. The separating face is produced extremely precisely in relation to the lead frame and therefore in relation to the positions of the conductor tracks or leads. The tolerance of the indirect positioning of the conductor leads via the separating face of the housing body therefore essentially corresponds to the extremely close fabrication tolerance of the lead frame.
A preferred embodiment of the method according to the invention provides that, a number of conductor leads initially remain connected to one another via intermediate sections in order to form a dam bar, the extension being formed on at least one of the intermediate sections. This has in particular the advantage that the isolation of the extension from the lead frames and the subsequent removal can be carried out in the course of a so-called dam bar cutting process (removal of the intermediate sections between the conductor leads). It is particularly advantageous if the isolation and removal of the extension are carried out in a joint operation with the dam bar cutting. The intrinsically already well managed steps of tailoring the lead frames (for example the dam bar cutting) can consequently be maintained in the conventional manner and the usual sequence.
According to another mode of the invention, which is particularly preferred in terms of production, provides the extension as a lug extending toward the lead frame center.
With regard to the positioning of the component, for example in a test socket, another mode of the invention is particularly preferred in accordance with which in each case an extension is provided in a corner area of the lead frame in such a way that, after the formation of the housing body, the extension is located in a corner of the housing.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for positioning a component mounted on a lead frame in a test socket, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.